INDIVIDUALITY DIFFERENTIALS AND BLOOD GROUPS 155 



to the action of tissue coagulins extracted from the macerated kidney tissue. 

 The further possibility has to be considered that in this case toxic substances 

 which were peculiar to the duck kidney or also to other duck tissue were ex- 

 tracted from the implanted material ; such toxins would in certain respects be 

 comparable to special poisons which are present in some amphibian tissues. 

 But substances of this kind are distinct from the species differentials. Con- 

 sidering all these data, there is no reason to attribute the effect observed by 

 Sandstrom to the organismal differentials of the duck, but the substances 

 responsible for it may represent a special kind of tissue differential. 



Returning to the consideration of the blood groups, the conclusions stated 

 above apply directly to the four primary blood groups ; they probably apply 

 also to the secondary factors (A and A x , P.M.N., Rh.) more recently found. 

 All these factors determine the agglutination in vitro of blood corpuscles of 

 one individual by the serum of another, as well as the results of transfusions 

 of whole blood or of plasma. But as stated, it is very likely that additional 

 factors will be discovered in the future also in human blood, and that the 

 human erythrocytes contain individuality differential constituents. It is con- 

 ceivable therefore that in some cases, in which transfusion of blood or of 

 plasma has led to injurious reactions, strange individuality differentials may 

 have been involved. 



It may then be concluded that the greater the number of factors which are 

 found as determiners of the agglutination and hemolysis of the erythrocytes, 

 the greater will be the probability that some, or even all. of these factors may 

 also be constituents of the individuality differentials and thus may be the same 

 as the factors which determine the interaction of tissues from different 

 individuals. However, if we restrict ourselves to a consideration of the four 

 original blood groups, which at first were the only ones known and analyzed 

 from this point of view, these cannot, in all probability, be identified with the 

 individuality differentials. This conclusion is in agreement with the experi- 

 ments which we have already cited, as well as with some other data which 

 may briefly be mentioned: (1) Brother and sisters may belong to different 

 blood groups, whereas, many entirely unrelated individuals of the same 

 species, and even members of different species, may belong to the same blood 

 group. This identity of blood groups in members of different species does not 

 improve the outcome of the corresponding heterotransplantations, which de- 

 pends on the character of organismal differentials. The individuality differ- 

 entials are graded according to the genetic similarity between the bearers of 

 these individuality differentials. (2) There is much evidence that homoiog- 

 enous individuality differentials in no case have become, through inbreed- 

 ing, absolutely identical with antogenous differentials. Even after many gen- 

 erations of brother-sister inbreeding there is still no complete identity of the 

 individuality differentials in members of the closely inbred strains, and there 

 are strong indications that reactions against slight disharmonies of grafts may 

 appear in the hosts a long time after the transplantation has taken place. 

 Furthermore, the strength of the response of the host against different organs 

 and tissues differs and by selecting an active organ and the proper time for 



